1. Field of the Invention
This invention relates to a process for producing hydrogen and more particularly to a process for producing hydrogen by reducing proton (H.sup.+) with viologen cation radical formed by irradiation, using metal complex of macrocyclic polydentate compound as catalyst.
2. Description of the Prior Art
In view of development of a new energy source for substitution of fossil energy, the formation of hydrogen and oxygen gases by decomposing water using solar energy attracts public attention recently. Particularly, hydrogen gas is expected to become a future energy source and many studies have been performed with respect to hydrogen. It is known that viologen is easily reduced when irradiated with visible light in the presence of suitable sensitizer and electron donor to produce its cation radical and that the cation radical reduces proton in the presence of catalyst such as colloidal platinum or palladium to produce hydrogen. The process described above, however, has some problem for practical uses since platinum and palladium are expensive and colloids of such metals have a very low stability against heat and light.
We studied a process for producing hydrogen in consideration of the above-mentioned problems and found that proton is efficiently reduced to produce hydrogen by adding metal complex of phthalocyanine (Pc), tetraphenylporphyrin (TPP), tetraazaannulene (TAA), hemiporphyrazine (Hp), salicylaldehyde ethylenediimine (Salen), acetylacetone ethylenediimine (Acacen), or derivatives thereof, or polymer in which the metal complex is held in the polymer chain, or polymer metal phthalocyanine complex as catalyst to a solution containing viologen cation radical, thus we completed this invention.